WASHINGTON (CNN) -- Efforts by two conservative groups to help President Bush by getting independent presidential candidate Ralph Nader on the ballot in the key battleground state of Oregon has prompted a complaint to the Federal Election Commission by a liberal watchdog group.

Citizens for Responsibility and Ethics in Washington (CREW) said phone banks encouraging Bush supporters to attend a Nader nominating convention last Saturday amounted to an illegal in-kind contribution to the Nader campaign by the Oregon Family Council and Oregon Citizens for a Sound Economy.

Bush's re-election campaign and the Oregon Republican Party were also named in the complaint for allegedly participating in the effort. The complaint alleges the groups worked together to promote Nader and siphon potential votes away from Sen. John Kerry, the presumptive Democratic presidential nominee.

Melanie Sloan, executive director of CREW, said the two groups, though non-profit, are still considered corporations, "and corporations are strictly prohibited from making contributions to political campaigns."

While the Bush campaign had no immediate comment, Nader spokesman Kevin Zeese called the allegations "absolute nonsense."

"We didn't work with any Republican groups or any corporations or non-profits trying to get people to come to our event," Zeese said. "We reached out to our constituency and got our people out there."

To get on the ballot, the Nader campaign has to get the signatures of 1,000 registered voters in one day or submit 15,000 signatures statewide. On Saturday, Nader supporters held a convention in Portland to try to get the necessary signatures.

While more than 1,100 people attended, the signatures are still being verified, so it is unclear if the effort was successful.

Whether Nader gets on the ballot in Oregon could be critical in deciding which candidate carries the state and its seven electoral votes. In 2000, Democrat Al Gore beat Bush by less than 7,000 votes in the state.

Published polls show Bush running neck-and-neck with Kerry, with Nader drawing 3 percent to 5 percent of the vote.

The Oregon Family Council is a conservative Christian group that opposes same-sex marriage and abortion rights. Oregon Citizens for a Sound Economy is the state chapter of a national anti-tax group headed by former House Majority Leader Dick Armey.

Both groups openly admit they urged supporters to show up at the Nader event.

"We called about 1,000 folks in the Portland area and said this would be an opportunity to show up to provide clarity in the presidential debate," said Matt Kibbe, president of CSE, who denied the the calls were coordinated with either the Bush or the Nader campaigns.

Kibbe said Nader "forces John Kerry to explain where he is on things.''

In its complaint, CREW also charged that the state GOP encouraged the Oregon Family Council to make the phone calls, which it said amounted to "illegally conspiring" with an outside group to evade a ban on state parties using soft money to send out public communications.

"What the Oregon Republican Party could not do directly, it could not do indirectly," the complaint said.

CREW also cited comments by Bush spokesman Steve Schmidt that campaign volunteers, though not paid staffers, may have made phone calls from the campaign's office. The costs of those calls, including the preparation of phone lists and scripts, should have been reported to the FEC as an in-kind contribution from the Bush campaign to Nader, which would be illegal if it amounted to more than $5,000, the complaint said.

Sloan also told CNN that she is convinced the phone banks were coordinated between the Bush campaign, the Oregon GOP and the two groups, saying "it can't be a coincidence ... that they're all making the same phone calls at the same time." However, she said it is unclear whether the Nader campaign was involved.

"If Ralph Nader gets on the ballot, he would pull thousands of liberal votes that would otherwise go to Kerry and perhaps cause President Bush to lose the election," read one script for the phone campaign, which CREW cited in its complaint.

CREW has previously filed complaints against both the Nader and Bush campaigns, alleging illegal assistance from tax-exempt corporations. Zeese, noting that the group has never moved against a Democrat, called it a partisan organization, and he accused Democrats of trying to interfere with the Nader signature drive.

Democrats have been trying to persuade Nader supporters not to back his independent bid this year, arguing that it will help Bush by dividing the liberal vote in closely fought states.